Wrapping machine

ABSTRACT

A wrapping machine for wrapping packages with stretch film has means at each side of a conveyor for gripping outwardly extending end wing members of the film on an advancing partially wrapped package. This means moves in a forwardly and downwardly arcuate direction and pulls the wing members to stretch the film taut over the package whereupon plow means folds the wings inwardly and upwardly against the bottom of the package for sealing.

United States Patent Inventor Erik 0. Vilen Niles, Ill. Appl. No. 872,069 Filed Oct. 29, 1969 Patented Jan. 4, 1972 Assignee Triangle Package Machinery Company Chicago, Ill.

WRAPPING MACHINE 10 Claims, 13 Drawing Figs.

US. Cl 53/378 Int. Cl 1365b 7/08, B651) 1 1/08 Field of Search 53/32, 33, 182, 184, 206, 209, 210, 228, 229, 230, 233, 378, 379, 388

[56] References Cited UNITED STATES PATENTS I 2,926,473 3/1960 Byland 53/379 X 3,537,235 11/1970 Pepmeieretal 53/210X Primary Examiner-Theron E. Condon Assistant ExaminerRobert L. Spruill Att0rneyJohnston, Root, OKeeffe, Keil, Thompson &

Shurtleff ABSTRACT: A wrapping machine for wrapping packages with stretch film has means at each side of a conveyor for gripping outwardly extending end wing members of the film on an advancing partially wrapped package. This means moves in a forwardly and downwardly arcuate direction and pulls the wing members to stretch the film taut over the package whereupon plow means folds the wings inwardly and upwardly against the bottom of the package for sealing.

PATENIEDJM 41912 3631.653

SHEEI 1 OF 4 FIG. I

ERIK O. VILEN QM M ATT'YS PATENTED JAN 41912 3,631,553

ERIK O. VILEN ATTYS PATENTEDJAN 41912 3.631.653

SHEET 3 OF 4 F1650 P M49 35% M... 4 .SC ily m limi l l i lllmll IN VIA UR.

i ERIK O. VILEN & 5 Z,/20-o4 Mae/g2,

ATT'YS PATENTEDJAN 41972 3,631; 653

SHEET 4 0F 4 FIG? ERIK O. VILEN ATT'YS WRAPPING MACHINE BRIEF SUMMARY OF THE INVENTION The invention relates broadly to package wrapping machines and is directed specifically to a machine embodying novel means for wrapping packages with stretch film. I-Ieretofore various types of film have been utilized in package wrapping machines such film being usually of a heat scalable type. In the use of such film various folding means such as end folders, down folders, and under folders have been utilized for folding the outwardly extending end wing members around the ends of the package end upwardly against the bottom thereof for sealing.

More recently a relatively new film has been introduced on the market which is stretchable and which has certain ad vantages in the wrapping of packages. Before the advent of this stretch film it was customary to use a shrink film which necessitated the use of a so-called shrink tunnel so that after the package was wrapped and sealed the film would then be caused to shrink thereupon resulting in a tightly wrapped package. One of the advantages of wrapping packages with a stretch film is that the use of a shrink tunnel for shrinking the film may be eliminated. Furthermore, heretofore, those wishing to use stretch film in wrapping packages could not do so automatically because of the unavailability of a machine to do so.

In utilizing the stretch film the package is partially wrapped in the usual way by folding a length of the film around the package thereby leaving outwardly extending end wing members. At this point, however, in order to provide a tightly wrapped package it is necessary to exert a pulling force on the extending wing members which will stretch the film taut over the package. It is then necessary to provide means for folding these wing members in the taut condition thereof inwardly and upwardly against the bottom of the package.

In view of the foregoing it is one of the principal objects of the present invention to provide a wrapping machine which is especially adapted for wrapping packages with a stretch film.

Another object of the invention is to provide a wrapping machine utilizing stretch film wherein the outwardly extending wing ends of the film around the package are caused to be stretched taut over the package as it is being advanced through the machine and then folded inwardly and upwardly in the taut condition against the bottom of the package.

Still another object is to provide a wrapping machine for wrapping packages with stretch film wherein a partially wrapped package having outwardly extending end wings is advanced along a support and wherein, during said advancement, the end wings are gripped and pulled downwardly to stretch the film taut over the package, and then folded inwardly and upwardly against the bottom of the package.

A still further and more specific object of the invention is to provide a novel form of film stretching means in a stretch film wrapping machine which includes a grooved wheel and a belt between which outwardly extending end wing members of a stretch film wrapping material is pinched as the package is advanced, whereby a downward and forward pull is exerted to stretch the film taut over the package. At or before the film is released, plows fold the stretched film inwardly and upwardly against the package bottom.

Other objects and advantages of the invention will become apparent upon reading the following description taken in conjunction with the accompanying drawings, in which FIG. 1 is a side elevational view of a wrapping machine embodying the present invention.

FIG. 2 is a top plan view of the machine shown in FIG. 1, such view being taken substantially along the plane of line 2- 2 of FIG. 1.

FIG. 3 is a longitudinal sectional view, partly in elevation, taken along the plane of 3-3 of FIG. 2, on an enlarged scale, but showing the lowering table of the machine in the lowermost position thereof.

FIG. 4 is a view similar to FIG. 3, taken along the plane of line 4-4 of FIG. 2, but showing the lowering table approaching the upper position thereof.

FIGS. 5a through 5d illustrate the progression of a package being wrapped with a stretch film as it is advanced through the gripping means which stretches the film.

FIGS. 6a through 6d are perspective views illustrating the end wing members of the film in various stages from the initial stage through the stretching stages to the point where the gripping means releases the film.

FIG. 7 is a fragmentary view similar to FIG. 5a but on an enlarged scale.

FIG. 8 is a detailed sectional view taken along the plane of line 8-8 of FIG. 7.

FIG. 9a is a fragmentary sectional view taken along the plane of line 9a-9a of FIG. 2 and illustrating one of the end wing members before it reaches the gripping means, and

FIG. 9b is a fragmentary sectional view taken along the plane of line 9b9b of FIG. 2 illustrating the initial contact of one of the end wing members against the bottom of the package which position must be reached prior to the film being released by the gripping means.

DETAILED DESCRIPTION The invention is disclosed herein in connection with an automatic wrapping machine, although it will be understood that the device for stretching the ends of the film around the package and forcing it upwardly against the bottom thereof may be used in combination with any wrapping machine or the initial partial wrap could be performed by hand. The wrapping machine which has been illustrated herein and to which the invention has been applied is described in greater detail in my earlier filed copending application Ser. No. 632,959, filed Apr. 24, 1967 and now US. Pat. No. 3,486,294. Such machine, therefore, will be described only briefly herein sufficiently to understand the general operation thereof since reference may be had to the aforesaid application for an understanding of the details.

Referring now more particularly to FIGS. 1, 2, 3 and 4 of the drawings the wrapping machine shown therein, for pur poses of illustration only, includes a frame member 1 at the upper part of which a web of wrapping material may be draped, such material being indicated at W. As far as the operation of the machine in general is concerned, this wrapping material may be any material suitable for wrapping packages, but as applied to the present invention such material is commonly known as the stretch film type.

It will be noted that the web of film W is draped over the rod 2 and is intended to be supplied from a roll of such material (not shown). The forward part of the web hangs downwardly between a platform 3 and a lowering table 4. In operation, a package P is placed on the platform 3 and is pushed through the hanging web of film by a pusher 5 so that the package is moved onto the lowering table 4 whereupon the leading edge of the film will be positioned along a part of the bottom of the package.

A bar is then caused to move downwardly behind the package and force the web downwardly a predetermined distance behind the package.

The lowering table 4 has secured thereto a pair of spaced downwardly extending legs 6. The table is caused to be raised and lowered by suitable mechanism operated from a drive shaft and is caused to remain in a substantially horizontal position by means of a parallelogram arrangement. This arrangement includes a pair of spaced upper arms 7 which are pivotally mounted at one end thereof, as at 8, to the leg 6. The opposite ends of the arms are mounted to rotate about the fixed shaft 9. The shaft 9 is mounted on the spaced supports 10, secured to the frame of the machine.

The bottom of the parallelogram consists of an elongated plate member 11 formed at one end thereof into the spaced arms 12, pivotally mounted as at 13, to the legs 6. This plate 11 extends between the supports and is pivotally secured between the ends thereof to the supports 10 by means of the elongated pivot pin 14 extending therethrough. The end of the plate 1! extending beyond the supports 10 has a tension spring 15 secured thereto and which is mounted on the frame normally urging the end of the plate downwardly and the table upwardly, thereby acting as counterbalancing means resulting in lessening the pressure of a cam follower against a cam on the drive shaft which causes the lowering table to move up and down. A substantially vertically extending link 16 is pivotally secured at its upper end to the plate 11 and the lower end thereof is suitably connected to a bellcrank lever (not shown) which is operated by a cam which causes the table to raise and lower.

The table 4 is provided with an out-feed pusher 17 so that after the package P has been pushed onto the table against the out-feed pusher 17, and the table lowered, this latter pusher will force the package off of the lowering table onto a support, as indicated in FIG. 3.

In the wrapping machine of the aforesaid copending application, the folder bar 18, which may be seen in FIGS. 3 and 4, will have moved downwardly to drape the film over the package and downwardly from the trailing edge thereof. A cutting knife 19 preferably provided with a serrated edge is suitably mounted to receive a wedge member 20 mounted transversely over the lowering table on a crossbar 21 at its ends on the rearwardly extending side arms 22. These arms are pivotally mounted on the machine frame to pivot about a point 23. A pivotal movement of these arms will cause them to raise and lower and carry with them the wedge member 20 mounted thereon. When this occurs the web of wrapping material will be cut and when the package is moved by the out-feed pusher 17 the then leading edge of the package is pushed through the web thereby folding it around the package and along a part of the bottom thereof. A shaft 24 extends between suitable bearing members 25 on the spaced upper bars 7 of the parallelogram which operates the raising and lowering of the table. A sprocket 26 is mounted on the shaft 24 for rotation and supports a chain 27 which constitutes the out-feed conveyor. This chain also passes around another sprocket 28 mounted on the shaft 9 heretofore described. As the table is moved between its lower and upper positions, carrying with it the shaft 24, it will likewise carry one end of the out-feed conveyor, which is mounted thereon, through the sprocket 26. A lug or pusher member 29 is affixed to the chain 27 and is so positioned thereon that at the proper time it will be moved against the rear edge of the package P to push the package along the length of the support, during which movement the film will be stretched and folded around the package as will be described in greater detail hereinafter.

The support for the package, after it is moved off of the table in its lower position, comprises two sets of rollers at opposite sides of the machine one of which is generally indicated by the numeral 30 and the other by the numeral 31 and may be seen in FIG. 2. The series of rollers 30 are mounted for free rotation on a support bar 32, and the rollers 31 are similarily mounted at the opposite side of the machine on a support bar 33. It will be noted that some of the rollers at each side of the machine, and particularly those indicated by the numeral 34, are longer than the other rollers and are provided with annular flanges 35. As will presently be seen, these flanges aid in guiding the package as it is advanced through the machine. Flows are provided at opposite sides of the machine to aid in guiding the package and in properly manipulating the ends of the material as the package is advanced through the machine. These plows have an initial upstanding portion 36 and 37 which are disposed at an angle and converge toward each other in the direction of the advancing package. These portions then merge with the remainder of each plow resulting in the spaced parallel upstanding portions 38 and 39 which are provided with the horizontal tapered underfolding portions 40 and 41.

The mechanism for pulling and stretching the wrapping material taut over the ends of the package may be seen in H65. 1, 2, 3, and 4 on a smaller scale, in FIGS. 50 through 5d on a slightly enlarged scale, and in FIG. 7 on a still greater enlarged scale.

When a package is wrapped in the normal way by merely folding the wrapping material around the package there will be remaining outwardly extending end wing portions which have to be properly tucked and folded under the bottom of the package. In the case of stretch film there must be provided some means for stretching the film taut over the top of the package before it is folded underneath. Any suitable means for pinching the ends of the material tightly enough to pull and stretch it may be used, but the mechanism disclosed herein and about to be described has been found to be the most effective, from the standpoint of simplicity and reliability. lt is desirable to effect this operation while the package is advancing along the support and it therefore becomes desirable to stretch the film by pulling it forwardly and downwardly. Chains or belts used together between which the wrapping material may be pinched have not proved to be very satisfactory because both are impractical for various reasons. While it has been determined that the most effective and simple means is to provide mating members which move together so that one member is received in a recess in the other member and the material pinched therebetween, nevertheless various modifications of the specific structure shown herein can be used, as will appear more fully hereinafter.

With these considerations in mind, the present invention, as shown herein for purposes of illustration, provides a grooved rotary member such as the wheel or pulley 42 having an annular groove 43 in the periphery thereof. A pulley 42 is mounted for rotation at each side of the support and conveyor on stub shafts 44. Also at each side of the machine each pulley 42 has associated therewith a mating member 45 adapted to be received in the groove 43. As shown herein the member 45 is an endless belt which passes around a driving pulley 46 mounted on a stub shaft 47. This belt also passes around an idler pulley 48 mounted for free rotation on a pin 49 located at the upper end of the bar 50 also mounted for free rotative movement on the shaft 44.

As may be seen, quite cleariy, in the various figures of the drawings, the belt and pulley are so positioned relative to each other that a part of one run of the belt is received within the groove 43 in the pulley under pressure. As the end wing members of the wrapping material are advanced through the machine they are guided between the belt and pulley at each side thereof where the pinching pressure is sufficient to prevent slippage of the film thereby effectively stretching the film taut.

The lower end of the bar 50 at each side of the machine has connected thereto a tension spring 51 through the pin 52, and the other end of the spring is suitably connected, as at 53, to a part of the machine frame.

The belt 45 is driven and also drives the pulley 42. Reference to FIG. 8 shows the preferred configuration of these mating parts wherein the belt 45 is tapered whereby the narrower side is received within the pulleys 46 and 48, while the wider side is received within the groove 43. Thus the inside of the belt is used for driving and the outside of the belt is used for pinching, whereupon any jamming of film between the two members will allow the belt to keep moving. If the pulley 42 were to be the driven member, then it would be possible to get slippage of the material when a jamming thereof occurs. Also the spring tensioning of the belt, by reason of the spring 51 will not only take care of any jamming which might occur, but also will keep the belt tight if it should stretch, and will maintain the pinching action between the two members in spite of any thickness of film or any wrinkles which might occur.

The belt 45 is driven by a motor 54 and this driving arrangement may be understood by viewing H08. 1 and 2. A motordriven gear reducer 54 is provided with an output shaft 55 on which is mounted a sprocket 56. A chain 57 passes around the sprocket 56 and a second sprocket 58 mounted on the shaft 59 which extends transversely of the machine as seen in FIG. 2 and which is mounted in suitable bearings in the machine frame.

If desired an idler sprocket 60 may be provided to maintain tension on the chain 57. A second and larger sprocket wheel 61 is also mounted on the shaft 59 around which a chain 62 passes. The upper end of chain 62 passes around the sprocket wheel 63 on shaft 64. These details of the drive mechanism may be more clearly seen by reference to FIG. 7. Shaft 64 also has mounted for rotation therewith a driving gear 65 which meshes with a pinion 66 on shaft 47. It will thus be evident that the motor 54 through the chain drives 57 and 62 will cause a clockwise rotation of the driving gear 65 and a counterclockwise rotation of pinion 66 and drive pulley 46, thereby imparting a clockwise rotation of the pulley 42.

FIGS. 5a through 5d and FIGS. 6a through 6d illustrate the action of the gripping and pinching means as the package P is advanced through the machine. In these figures the package has been partially wrapped with the wrapping material W, which in this case is a stretch film. This initial wrap, which may be made either by hand or by the mechanism heretofore described leaves the outwardly extending end wing members 67. These wing members extend outwardly and will be intercepted by the gripping means as the package advances. FIG. 5a shows the package in its partially wrapped state, as it is about to be received between the pinching members of the gripper. FIG. 5b shows the package as it has been advanced and where the wind members have been initially gripped, the condition of the end wing members being substantially as illustrated in FIG. 617.

As the package continues to advance the entire outwardly extending ends 67, at each end of the package, will have been pulled downwardly and forwardly as shown in FIGS. 56 and 6c. This action then stretches the film taut over the package.

It should be here noted that the speed of the driving mechanism for the mating members drives thesemembers at a rate of speed such that when the wrapping material is first gripped thereby the package will be pulled forwardly away from the lug 29 of the conveyor chain which has moved the package to such initial gripping position. This is desirable since otherwise, if the pusher lug 29 were to move faster than the package is advanced by the gripper means, the tray of the package might bend or crack under the resulting opposing forces. In other words, the film is gripped so tightly that if the lug on the conveyor were to attempt to push the package faster than the gripping means allows it to move, a greater force would be exerted on the rear of the package, possibly damaging the tray. After the end wing members of the wrapping material have been released from the grippers, then the conveyor lug may again advance the package the remainder of the way through the machine between the two plows which then perform the under folding step.

In this connection, reference is made to FIGS. 9a and FIG. 9b where it will be noted that initially the end wing members 67 have been guided over the flanges 35 of the rollers and under the side plows 37. As the package advances and the gripping members pull downwardly to stretch the film over the package, the plows will be approached. The horizontal flanges 40 and 41 of the plows are positioned to fold the stretched ends of the wrapping material inwardly and upwardly against the bottom of the package. It is important that the gripping members not release the film until at or after the time at which the wing members contact the bottom of the package by action of the plows.

If the grippers were to release the film before the ends had contacted the bottom of the package some of the stretch would be relieved and a tightly wrapped package would not result. Thus the position of the plows and the timing is such that the end wing members are retained between the gripper members at least until the plows fold the material inwardly to the initial contact with the underside of the package as shown in FIG. 9b.

Stretch film is normally tacky and will stick to itself temporarily but it is still necessary to heat-seal the completely wrapped package. For this purpose a heated table or belt 68 is provided onto which the completely wrapped package is advanced. This feature is well known and forms no part of the present invention, but it may here be noted that when the package has been moved onto the support 68, the heat provided thereby is sufficient to seal the under folded ends of the material against the bottom of the package, at which time it may either be removed by hand or conveyed to a suitable receptacle.

The natural tackiness of the material will be sufficient to hold the package wrapped tightly from the time it leaves the plows until it reaches the heated support member 68 for sealing.

It will thus be evident, from the foregoing, that an effective gripping means has been provided for pinching the outwardly extending ends of a stretch film wrapping material around a package and pulling the material forwardly and downwardly so that it is stretched taut across the package.

One of the basic considerations which makes this general concept simple but effective is the contoured path through which the film travels as it is being stretched, Note that this path from the point in initial gripping to the point of release is not a straight line, but is contoured in the direction of the belt. This enables greater pinching pressures to be exerted between the two gripping members by relatively simple apparatus.

The gripping members could consist of a chain and sprocket wheel instead of the belt and grooved pulley, if desired, or two belts or two chains, or a belt and a chain. Likewise, a series of rollers, with or without a belt thereon, could be substituted for the pulley 42 in the contoured line between the gripping and releasing points and a belt or chain used in cooperation therewith.

While the cross section of the belt is preferably frustoconical, as shown, it could assume any other shape, such as square, round, or flat, and operate successfully.

Because of the tacky or sticky nature of the film, it was necessary to provide a support means for the package as it is advanced through the machine which would afford the least amount of friction. It has been found that if the rollers 30 and 31 are formed of nylon, and the plows are coated with an antifriction substance, such as Teflon, this will give the least resistance to movement of the package through the machine.

Changes may be made in the form, construction and arrangement of parts from those disclosed herein without in any way departing from the spirit of the invention or sacrificing any of the attendant advantages thereof, provided, however, that such changes fall within the scope of the claims appended hereto.

The invention is hereby claimed as follows:

1. In a wrapping machine for wrapping packages with a stretch film,

a. support means for supporting a package partially wrapped with stretch film, wherein end wing members formed of the film extend outwardly beyond the ends of the package,

b. means for advancing a partially wrapped package along said support,

c. gripper means adjacent said support at each side thereof for gripping the wing members along an extended path and for pulling forwardly and downwardly thereon in an arcuate path while the package is advancing, and then releasing said wing members, thereby stretching the film taut over the package,

(1. plows at each side of said support in advance of said gripper means and having converging underfolding means thereon adapted to fold said wing members inwardly and upwardly against the underside of the package as the package is advanced along said support, and

e. the rear ends of said underfolding means being positioned with respect to the release point of said gripper means whereby said gripper means will not release the stretched film before said underfolding means have moved the wing members into contact with the package bottom.

2. The combination of elements defined in claim 1, wherein each said gripper means includes a pair of members, at least one of which is movable, which are pressed together and carry the wing members in a generally downward contoured path and between which the wing members are pinched.

3. The combination of elements defined in claim 1 wherein said means for advancing the package along said support comprises a continuously moving pusher member.

4. The combination of elements defined in claim 2, and drive means for driving said pair of members with respect to said advancing means at such speed as to move the package along said support faster than the speed of movement of said advancing means when the wing members are initially pulled taut by the gripper means.

5. The combination of elements defined in claim 1, wherein said support means includes a plurality of longitudinally spaced nylon rollers at each side thereof upon which the package is supported and advanced.

6. In wrapping machine for wrapping packages with a stretch film,

a. support means for supporting a package partially wrapped with stretch film wherein end wing members formed of the film extend outwardly beyond the ends of the package,

b. means for advancing a partially wrapped package along said support,

c. a pair of mating members pressing against each other along a generally downwardly and forwardly extending arcuate path positioned at each side of said support and between which the wing members are pinched as they are advanced, whereby the film is pulled downwardly and forwardly in an arcuate path and stretched taut over the package,

d. means to fold the wing members inwardly and upwardly in their taut condition against the bottom of the package, and

e. means to seal the wing members against the package bottom.

7. The combination of elements defined in claim 6, wherein each said pair of mating members includes a grooved rotary member and an endless driving member, the outer surface of a portion of one run of said endless driving member being received in the groove of said rotary member for a predetermined distance along the length of the periphery thereof.

8. The combination of elements defined in claim 6, wherein each said pair of mating members includes an endless driving member and a grooved rotary member, a driving pulley and an idler pulley around which said driving member passes, said grooved rotary member positioned to receive a length of the outer surface of said endless driving member in the groove thereof and be driven thereby.

9. The combination of elements defined in claim 8, including yieldable tensioning means for said idler pulley to hold said endless driving member under tension and to maintain a pinching action against the wing members between said driving member and said grooved rotary member.

10. The combination of elements defined in claim 7, wherein said grooved rotary member is a wheel, and said endless driving member is a belt. 

1. In a wrapping machine for wrapping packages with a stretch film, a. support means for supporting a package partially wrapped with stretch film, wherein end wing members formed of the film extend outwardly beyond the ends of the package, b. means for advancing a partially wrapped package along said support, c. gripper means adjacent said support at each side thereof for gripping the wing members along an extended path and for pulling forwardly and downwardly thereon in an arcuate path while the package is advancing, and then releasing said wing members, thereby stretching the film taut over the package, d. plows at each side of said support in advance of said gripper means and having converging underfolding means thereon adapted to fold said wing members inwardly and upwardly against the underside of the package as the package is advanced along said support, and e. the rear ends of said underfolding means being positioned with respect to the release point of said gripper means whereby said gripper means will not release the stretched film before said underfolding means have moved the wing members into contact with the package bottom.
 2. The combination of elements defined in claim 1, wherein each said gripper means includes a pair of members, at least one of which is movable, which are pressed together and carry the wing members in a generally downward contoured path and between which the wing members are pinched.
 3. The combination of elements defined in claim 1, wherein said means for advancing the package along said support comprises a continuously moving pusher member.
 4. The combination of elements defined in claim 2, and drive means for driving said pair of members with respect to said advancing means at such speed as to move the package along said support faster than the speed of movement of said advancing means when the wing members are initially pulled taut by the gripper means.
 5. The combination of elements defined in claim 1, wherein said support means includes a plurality of longitudinally spaced nylon rollers at each side thereof upon which the package is supported and advanced.
 6. In wrapping machine for wrapping packages with a stretch film, a. support means for supporting a package partially wrapped with stretch film wherein end wing members formed of the film extend outwardly beyond the ends of the package, b. means for advancing a partially wrapped package along said support, c. a pair of mating members pressing against each other along a generally downwardly and forwardly extending arcuate path positioned at each side of said support and between which the wing members are pinched as they are advanced, whereby the film is pulled downwardly and forwardly in an arcuate path and stretched taut over the package, d. means to fold the wing members inwardly and upwardly in their taut condition against the bottom of the package, and e. means to seal the wing members against the package bottom.
 7. The combination of elements defined in claim 6, wherein each said pair of mating members includes a grooved rotary member and an endless driving member, the outer surface of a portion of one run of said endless driving member being received in the groove of said rotary member for a predetermined distance along the length of the periphery thereof.
 8. The combination of elements defined in claim 6, wherein each said pair of mating members includes an endless dRiving member and a grooved rotary member, a driving pulley and an idler pulley around which said driving member passes, said grooved rotary member positioned to receive a length of the outer surface of said endless driving member in the groove thereof and be driven thereby.
 9. The combination of elements defined in claim 8, including yieldable tensioning means for said idler pulley to hold said endless driving member under tension and to maintain a pinching action against the wing members between said driving member and said grooved rotary member.
 10. The combination of elements defined in claim 7, wherein said grooved rotary member is a wheel, and said endless driving member is a belt. 